Water level sensor

ABSTRACT

A sensor, such as a hydrostatic water level sensor, includes a pressure sensor, a vent, a vent tube connecting the vent to the pressure sensor, and a fabric covering the vent. The pressure sensor is submersible in a liquid to be measured and the vent is configured to be outside the liquid. The fabric covers the vent and is both waterproof and breathable, e.g., Gore-Tex®. The vent may be integrated into an electrical connector for the pressure sensor, and the electrical connector may provide IP-65 protection. The sensor may be particularly be employed in an aeroponic plant growth system where the fabric prevents mist from blocking the vent and/or vent tube.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent document is a claims benefit of the earlier filing date of U.S. provisional Pat. App. No. 62/631,041, filed Feb. 15, 2018, which is hereby incorporated by reference in its entirety.

BACKGROUND

Indoor systems have been developed for growing plants. For example, hydroponic systems can grow plants without soil, e.g., with roots suspended in air, liquid, or other media and plant nutrients provided in an aqueous solution that may be applied to the roots. An automated or software-controlled hydroponic system that employs aeroponic techniques, e.g., with plant roots predominantly suspended in the air and nutrient solution delivered to the roots in a mist, is described in U.S. Pat. App. Pub. No. 2016/0021836, entitled “Aeroponic Growth System Wireless Control System and Methods of Using,” published Jan. 28, 2016, which is hereby incorporated by reference in its entirety.

Automated plant growth systems that may be software controlled generally require many types of sensors to measure operating parameters of the system. For example, a sensor may be needed to measure the level of water in a reservoir, and a hydrostatic water level sensor may be used to measure water levels. Hydrostatic water level sensor typically measure a difference between the pressure applied by water and the pressure applied by ambient air. The pressure difference particularly indicates the weight of water above the location where water pressure is measured, and the height of the water above the location of the pressure measurement is proportional the measured pressure difference. These hydrostatic sensors require access to ambient air pressure for accurate measurements.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows partially transparent perspective view of one implementation of a water level sensor.

FIG. 2 shows a hydroponic system employing a water level sensor.

The drawings illustrate examples for the purpose of explanation and are not of the invention itself. Use of the same reference symbols in different figures indicates similar or identical items.

DETAILED DESCRIPTION

A hydrostatic water level sensor employs a pressure sensor, a vent to ambient air, and a vent tube. In particular, a level or depth of a liquid may be determined from a difference between the ambient air pressure and the pressure at the pressure sensor within the liquid. Such water level measurements are often needed in automated hydroponic systems. However, hydroponic systems, particularly aeroponic systems, often create mist and a high chance of exposing the vent of a water level sensor to liquid water. Without protection, the water exposure can block the vent of a hydrostatic water level sensor and prevent accurate measurements of water level. In accordance with an aspect of the invention, the vent of hydrostatic water level sensor can be covered with a breathable and water repellant fabric, which prevents mist from entering or blocking the vent but permits sufficient air flow for accurate water-level measurements. In accordance with a further aspect of the invention, the vent and fabric covering can be incorporated in an electrical connector for the hydrostatic water level sensor.

FIG. 1 shows a partially transparent view of a water level sensor 100 in accordance with one implementation of the invention. Water level sensor 100 includes an electrical connector 110 and a submersible pressure sensor 120 that are connected by wires 132 and a vent tube 142. In use, electrical connector 110 may be kept out of water or other liquid being measured, and a submersible pressure sensor 120 may be submerged in the water or other liquid.

Connector 110 includes an electrical socket 130 and an air vent 140. Electrical socket or plug 130 is generally used in a damp environment and near water, and socket 130 can be configure to provide IP-65 ingress protection. Ingress Protection (IP) ratings are defined by international standard EN 60529 that defines levels of sealing effectiveness of electrical enclosures against intrusion from foreign bodies (tools, dirt etc) and moisture. See British BS EN 60529:1992, European IEC 60509:1989. IP-65 means that socket or plug 130 when connected to a complementary plug or socket (not shown) provides protection against entry of harmful dust and protection from water spray from any direction. Socket or plug 130 further provides electrical connectivity to wires 132 that provide waterproof connections to submersible pressure sensor 120. FIG. 1 shows an example shape for socket 130 when four wires 132 are used for signal transmission. More generally, the number of wires 132 and the shape of socket 130 may vary according to the type of submersible pressure sensor 120 and may available choices for socket features.

Vent 140 is at the end of vent tube 142 and is covered with a waterproof and breathable fabric 150. Fabric 150 may be in the shape of a loop, band, or strip that wraps around or adheres to a casing of connector 110 and covers vent 140. Fabric 15 is “breathable” so that air can pass through fabric 150, and the air pressure in vent tube 142 and at submersible sensor 120 is substantially the ambient air pressure above the liquid being measured. Fabric 150 is also waterproof to prevent liquid water from entering vent 140 and to repel liquid water that might otherwise cling to other fabrics. A waterproof and breathable fabric such as a stretched polytetrafluoroethylene (PTFE) fabric, which is commercially available Gore-Tex®, may be suitable for fabric 150. Some other suitable waterproof and breathable fabrics are available under brand names including eVent®, MemBrain®, Polartec® NeoShell®, Polartec® Power Shield® Pro, Dry.Q™ Elite, DryVent® (Formerly Hyvent®), H2No®, PreCip™, and Pertex® Shield+/AP.

Sensor 120 may be a submersible pressure sensor that generates an electrical signal indicating a different between the pressure in vent tub 142 and the pressure from liquid that may be surrounding submersible sensor 120. Many types of submersible pressure sensors are commercially available, and different types of sensors 120 may employ different numbers of wires 132 for electrical signal transmission, for example, two wires 132 for a 4-20 mA output signal, three wires 132 for 0-5/10 VDC output signal, or four wires 132 for a RS485 output signal. As noted above, FIG. 1 illustrates an example using four wires 132, but many other options are possible.

FIG. 2 shows one implementation of a hydroponic system 200 using water level sensor 100. In the illustrated implementation, hydroponic system 200 is an aeroponic system used for growing plants 210. System 200 particularly includes an enclosure 220 such as a tub or reservoir that holds water 230 and provides air space 232 for roots 212 of plants 210. As shown, roots 212 may extend through and be supported net cups 224 or other media that are held in a removable tray 222, but roots 212 are otherwise predominantly suspended in air space 232 above a top level 234 of water 230.

System 200 uses a pump 240 to pump water 230 to misters 242 that spray a mist of water 230 on to roots 242, and excess water from roots 212 may dip back into water 230. Water 230 generally includes dissolved nutrients for plants, and the term “water” is used broadly here to include nutrient solutions. System 200 further includes a dosing system 250 and a controller 260. Dosing system 250 may contain canisters of plant nutrients and may be connected to a facility water supply, and controller 260 is capable of executing software to control operation of dosing system 250, for example, so that water 230 contains desired concentrations of nutrients. The nutrient concentrations in water 230 may be specified by a software-defined growth plan and tailored for the type of plants 210 being grown and the growth stage of plants 210. Controller 260 may further control over-plant systems 270 such as lighting 272, heating, ventilation, and air conditioning (HVAC) systems 274, and other system (not shown) that may provide for the needs of plants 210. To control system 200 and provide for the needs of plants 210, controller 260 generally requires feedback or measurements from multiple sensors in system 200. For example, sensor 276 outside of enclosure 220 may measure the temperature, light spectrum and intensity on plants 210, and carbon dioxide (CO₂) concentration around plants 210 or may measure characteristics of plants 210 such as plant heights, shape, or color. Sensors 256 in enclosure 220 may measure characteristics of water 230 such as temperature, conductivity, pH, or other chemical properties of water 230.

Water level sensor 100 may be mounted in enclosure 220 to measure water level 234, i.e., to determine the location of the interface between water 230 and air 232, which indicates the amount of water 230 in enclosure 220. As described above, connector 110 of water level sensor 100 is located in air 232 and submersible pressure sensor 120 is in water 230, and vent tube 142 and wires 132 extend from connector 110 to pressure sensor 120. Mist produced in aeroponic systems is often a fine mist that can travel significant distances in air space 232. Accordingly, during use, mist from misters 242 may fall on connector 110 and particularly on vent 140 in connector 110. Fabric 150, which is waterproof and breathable, covers vent 140 and prevents liquid water from entering or blocking vent 140 but also allows ambient air pressure through vent 140 and vent tube 142 to pressure sensor 120. Pressure sensor 120 generates a measurement signal indicating the difference between the ambient air pressure in vent tube 142 and the pressure that water 230 applies to pressure sensor 120. The pressure difference is equal to the weight of water pressing on pressure sensor 120, and given the known density of water 230, sensor 120 or controller 260 can determine the height of water 230 above pressure sensor 120 and thereby measure water level 234.

Although particular implementations have been disclosed, these implementations are only examples and should not be taken as limitations. Various adaptations and combinations of features of the implementations disclosed are within the scope of the following claims. 

What is claimed is:
 1. A system comprising a sensor that includes: a pressure sensor that is submersible in a liquid to be measured; a vent configured to be outside the liquid; a vent tube extending from the vent to the submersible sensor; and a fabric covering the vent, the fabric being waterproof and breathable.
 2. The system of claim 1, wherein the pressure sensor generates a measurement signal indicative of a different between an air pressure in the vent tube and a liquid pressure on the pressure sensor.
 3. The system of claim 1, further comprising: an electrical connector in which the vent resides, the vent tube extending from the electrical connector to the pressure sensor; and signal wires extending from the pressure sensor to the electrical connector.
 4. The system of claim 3, wherein the electrical connector protects an electrical connection from water spray.
 5. The system of claim 4, wherein the electrical connector is IP-65 rated.
 6. The system of claim 1, wherein the fabric comprises stretched polytetrafluoroethylene.
 7. The system of claim 1, wherein the fabric comprises Gore-Tex®.
 8. The system of claim 1, wherein the system is an aeroponic plant growth system, and the vent deployed in a location subject to mist produced in the aeroponic plant growth system, the fabric protecting the vent from being block by liquid from the mist. 